Present-day screen printers operate quite rapidly and thus turn out printed sheets or web sections at a fast rate. For efficient operation, that rate must be matched by the throughput of a drying oven to which the freshly inked substrates are delivered and which they must leave in a state suitable for stacking or coiling, as the case may be. An advantageous type of drying oven is equipped with one or more sources of radiant energy, generally infrared or ultraviolet radiation, which for simplicity will be referred to hereinafter as lamps. Uniform drying requires that the inked substrate should move at consant speed past a lamp or row of lamps extending across its full width, the lamp or lamps irradiating at any instant a well-defined zone of the sheet. The time exposure of an elemental area of the substrate to the infrared or ultraviolet rays is determined by the extent of the irradiated zone in the direction of sheet motion and is inversely proportional to the speed of that substrate. With a given average ink density, therefore, the required minimum drying time imposes a limit on the speed of travel of the substrate through the oven. The exposure time can be foreshortened by enhancing the power of the lamp or lamps, yet this is risky since it may cause overheating of the more sparsely inked areas and may thus deform the substrate or otherwise damage the print.